The present invention generally relates to a vehicle passenger seat belt system, and more particularly a seat belt system which provides enhanced passenger comfort through electronic belt tension control.
Generally, known seat belt systems typically combine a tensioner and a pretensioner to control seat belt tension. Typical belt tensioners operate by exerting a constant belt tension through spring loading. The spring biasing is designed to partially remove slack to keep the belt snug against the occupant's chest, while not tensioning the belt hard enough to overcome the slack caused by heavy clothing. Because the belt tension is constantly applied, the belt tension exhibited by typical tensioners tends to be an irritant which may cause some occupants not to wear belts, or to otherwise arrange a manner of tension relief which defeats the function of the chest-restraint belt because of the creation of excessive slack.
Known pretensioner arrangements have also proven to be unsatisfactory. More specifically, typical seat belt pretensioners are usually in the form of a pyrotechnic device which utilizes an explosive gas generator to activate and power a mechanism which winds up the slack in the lap and chest belts. However, typical seat belt pretensioners have limited ability to reel in belt length, because winding depends on the force and stroke of a piston activated by the pyrotechnic device. Therefore, if as noted above the belt has been extended to relieve irritation, the problems of known belt tensioning systems is compounded by the fact that the pretensioner may be unable to take up sufficient length to afford optimum occupant protection.
In addition to the above described deficiencies, known occupant restraint systems are unable to remind occupants that they are out of optimal position to receive protection from the vehicle occupant restraint system.